With development of communications technologies, chargers of mobile terminals such as chargers of a cell phone, a tablet computer, and the like are all in a form of a universal charger, for example, a form in which one Universal Serial Bus (USB) data cable and one power adapter with a USB port are included so as to resolve a problem that chargers of multiple types of mobile terminals are incompatible.
A current power adapter is connected to a USB Type A plug of a standard USB interface connection line using a USB type A socket, and the other end of the USB interface connection line generally takes the form of a Micro USB interface and is connected to a mobile terminal. When charging is being performed, the power adapter outputs a fixed voltage (the voltage is obtained by conversion from an alternating current and is also generally used as a rated charging voltage of the to-be-charged mobile terminal) such as a voltage of approximately 5 volts (V) so as to charge the mobile terminal using the USB interface connection line connected to the power adapter. Because of contact impedance in a cable of the USB interface connection line and a line loss of the cable, a charging voltage that finally reaches the mobile terminal is less than the rated charging voltage and consequently a charging time is longer than a theoretical charging time.